When you looking to make a copy of a Roman mosaic you do need to look out for those that have been restored. This example is from from the Archaeological Museum in Barcelona. I don't recall anything saying it had been subject to restoration but if you look at the figures eyes and hair I would say it has.
If a mosaic has been restored it should be made very clear which areas are original and which are guesswork on the part of the restorers. Here you have a figure looking over to the left yet his eyes are set as if he would be face on to the viewer.